Rabies is virtually non-existent in North America, but it's still a blight in many parts of the world, including South America. The disease, which is commonly transmitted by bats, is almost always fatal. But a recent study conducted in Peru is suggesting that native people there may have developed an immunity to the virus by getting bitten by vampire bats. If true, the discovery could have serious implications to the development of vaccines — and even a cure.

News of this study comes to us from Marissa Fessenden of Scientific American. She describes how the vampire bats, who bite humans while they're sleeping, may have passed along small amounts of the virus over time. Similar to how a person can develop an immunity to snake venom, the low-dose exposures may have induced the rise of natural anti-bodies in the Peruvians.

Rabies jumps from host to host through the bite of an infected animal. The virus itself travels from the wound to the brain through an unusual highway. Instead of swirling through the blood, it creeps along nerve fibers. This slow progress explains the variable timing of symptoms following a bite: the farther the bite is from the brain, the longer the virus must crawl. The time lag also gives bite victims the opportunity to seek treatment. A vaccine and treatment with rabies-specific antibodies, even after a bite, arms the immune system to fight off the virus. Contrary to popular belief, the post-exposure treatment for previously unvaccinated people is just four shots to the upper arm over two weeks. People who have been previously vaccinated for protection against the virus only need two shots. The critical moment is when the virus reaches the central nervous system (CNS). Without treatment, weeks or months after an attack the virus triggers a full-blown CNS infection, complete with slavering, snarling, aggression and hydrophobia. At this point, it is usually too late for even the best medical treatment.

The study shows that rabies is not always lethal. This understanding, if backed and deepened by further studies, could lead to new treatments. The work implies that some people escape infection after exposure to a small amount of the virus, but [Amy] Gilbert says it is not clear from the researcher's work if the Peruvians developed true immunity to the virus. Instead the presence of antibodies indicates possible previous non-fatal infection. For now, prevention is the most effective strategy to combat rabies.

Another possibility is that the native population has developed genetic resistance to rabies — but no evidence exists for this claim. The researchers hope that the discovery, if confirmed, will inspire the development of novel therapeutics and a cure to rabies — a disease that kills 55,000 people each year.